The invention relates generally to electromagnetic interference and in particular, to reduction of common-mode noise.
Electronic devices may experience serious operating difficulties when subjected to unintended electromagnetic noise. Electromagnetic noise that interferes with the normal operation of a device, is generally known as electromagnetic interference (EMI). In order to ensure the reliable operation of electronic devices it is desirable that EMI be reduced to a minimum.
The manner in which EMI is suppressed is dependent on the nature of the interference. There are two ways undesirable noise can propagate in signal transmission paths: one is differential-mode interference, and the other is common-mode interference. Differential-mode interference causes the potential on one side of a signal transmission path to be changed with respect to another side. With this type of interference, the interference current path is wholly in the signal transmission path.
Common-mode interference appears between two signal transmission paths and a common reference plane (ground), and causes the potential of both sides of the transmission path to be changed simultaneously and by the same amount relative to the reference plane. Common-mode noise may be caused by an electric (capacitive) or magnetic (inductive) field when interference is induced in both signal transmission paths equally. Noise voltages developed may be the same in both transmission paths.
Common-mode filtering typically uses multiple filter assemblies in series to achieve the desired filtering wherein additional multiple filter assemblies contribute to additional cost, increase size and weight of the total filter assembly which is especially disadvantageous for volume and weight constrained applications. Further, working environments wherein aerospace applications require substantial attenuation of common-mode noise in multiple conductors with reduced weight and size. The common-mode performance of the filters is not sufficient.
Therefore, it is desirable to provide an apparatus that is capable of attenuating common-mode noise with decreased weight and minimal environmental impact.